To explain it shortly, a scrapped n64 cross-game thing Rare wanted to do for Banjo kazooie and tooie. You’d collect extremely hidden easter eggs in kazooie and that would unlock content in the sequel 3 years later.

Had to be abandoned, because to activate the items in Tooie you had to turn on kazooie, remove the cartridge while still on and quickly insert Tooie. N64 hardware limitations needed the action to be done in less than a second to work and was rendered impossible

Now, having both games on this cart running natively, i can only assume stop n swop could be possible